This invention relates to a printer for use in data processing apparatus, more particularly to a printer capable of readily mounting a deposit pass book of the type foldable in the longitudinal or lateral direction, so as to clearly print the amount of money.
Among the printers utilized in this field there are typing bar type and single element type but each of them is not satisfactory because of its low printing speed. Among improved printers that can print many types of letters and symbols, have high operating speed, and small noise and are of low price may be mentioned wire impact dot matrix type but in these types it is necessary to maintain the gap between a printing head and the surface of a recording medium, that is paper to be about 0.3 to 0.6 mm so that it is difficult to print satisfactory on the surface of a recording medium having different thickness, for example one sheet of a slip or a pile of slips and bank passbooks. For the purpose of eliminating these difficulties and readily mounting and dismounting the recording medium an improved printer has been proposed as described in the specification of Japanese patent application No. 90637 of 1974 in which a platen is retracted at the time of mounting and dismounting the recording medium and at the time of shifting lines and the surface of the medium is urged against a receptor which holds the recording medium at a suitable printing position. According to said patent application one end of a platen supporting lever is secured to the platen and the other end of the lever is pivotally journalled for bringing the platen toward and away from the recording medium. As a consequence, the platen moves along an accurate path so that when the thickness of the medium varies uniform printing cannot be ensured because the surface of the platen is not always in parallel with the surface of the recording medium. To decrease the inclination of the surface of the platen with respect to the recording medium, it is necessary to increase the length of the supporting lever which not only increases the occupation space but also reduces the rigidity. For the purpose of decreasing the amplitude of the oscillatory motion that is the amount of the lateral movement between the pressed state and the separated state of the platen it is desirable to locate as near as possible the center of the swing supporting lever aligned on a plane of the platen upper surface. Such arrangement, however, is difficult to construct because of the presence of a line shifting mechanism. Furthermore, as the supporting lever is pivotally journalled it is necessary to supply lubricating oil to the bearing portion to assure smooth movement and to prevent wear thereof. Since such bearing is located near the path of movement of the recording medium dust tends to deposit on the bearing.
According to said patent application, the platen is driven by a solenoid coil. As described in that application, the solenoid coil has many disadvantages in that it produces mechanical shocks and noise, damages pressure sensitive paper and that it is difficult to control the operating speed. Further in order to maintain the platen in engagement with the receiving member it is necessary to continuously energize the solenoid coil or to provide some mechanism to maintain such engagement. The latter mechanism requires a releasing member for separating the platen, thus complicating the construction and decreasing the reliability.